Active devices employed as microwave amplifiers are typically designed to maximize overall gain. Conjugate matching networks are designed to interface microwave signals leading into the active device responsible for amplification, and the same for signals exiting the device. The matching networks are typically static, either via design or with post-fabrication tuning, in which reactive or resistive properties of the matching networks are tuned to optimize a property of the amplifier. Tuning may be accomplished, for example, by removing bond wires or scribing connections that lead to reactive or resistive elements to change net matching properties of the conjugate matching circuits. The amplifier matching networks then remain in a static state once this tuning is performed.
Rapid changes in properties of the active device, e.g., in response to the onset of heating effects, as well as other physical properties, result in changes to the amplifier performance. This can happen, for example, in a cell phone when suddenly the transmitted carrier power needs to increase. This increases the current through the amplifier and can lead to a change in amplifier performance. The timescales can be quite rapid and result in changes to the scattering parameters (S-parameters) (S11 S12 S21 S22) of the amplifier as well as its nonlinear properties.